1. Technical Field of the Background
The present invention relates to an apparatus and methods for transferring the workpiece in a transfer press machine, in which the operation of transferring the workpiece is carried out by a combination of a rack and pinion, etc.
2. Prior Art
A conventional transfer press machine known in the prior art uses a system with a cam mechanism in which the dies are driven up and down in synchronism with the transfer of the workpiece. Recently, however, a system using a combination of a servo motor and a rack and pinion drive, etc., has been proposed to replace the system with a cam mechanism for transferring the workpiece, because there has been a demand for higher operating speeds in transfer press machines.
FIG. 1 is a schematic view showing such an example of a conventional system. In the transfer press machine 1, a main press unit 2 is configured with a bed 3 arranged along a press line L, a specified number of uprights 4 located opposite each other along the press line on the bed 3, and a crown 5 installed on the upper surface of the uprights 4. In addition, slides 7, carriers 8, and bolsters 9 are installed and arranged between the uprights 4; an upper die 6 is mounted on the lower surface of each slide for pressing and processing the workpiece, such as a door for an automobile, and can freely be raised and lowered by means of an up and down device, not illustrated, housed in the crown 5, and a lower die 10 is installed opposite the upper die 6 on the top of each bolster 9, which is mounted on the carrier 8 on the bed 3.
In addition, a pair of lift beams 13 are provided and arranged opposite each other and parallel to the press line L alongside the dies, and can be driven up and down by servo motors 11 and rods 12. Furthermore, underneath each lift beam 13, a feed beam 14 is hung and arranged in a manner that it can move freely in the horizontal direction along the press line L, while the beam 14 can be raised and lowered integrally with the lift beam 13. The feed beams 14 are supported by a plurality of cam followers 15 that grip the upper and lower surfaces of rails 16 provided on both sides of the lift beams 13, and can travel along them. Also, cross bars 18 are installed laterally on the feed beams 14 at the same intervals as those in which the dies are arranged, in the direction orthogonal to the press line L, and workpiece holders 19 are mounted on the cross bars 18 and on which workpieces are hung in order to carry them in and out of the lower dies 10.
In addition, on the upstream side of the inlet of the main press unit 2 (left side in FIG. 1), feed and transfer equipment 25 is arranged and comprised of a servo motor 21 that drives the feed beams 14 which are free to move horizontally in the direction of the press line L, a pinion 22 driven and rotated by the servo motor 21, and a rack beam 24 on the upper surface of which there is a rack 23 engaging with the pinion 22. In addition, a connecting rod 27 with a predetermined length (radius) R is connected to a bracket 26 provided on the lower surface of the rack beam 24 and to a feed beam 14, via connecting pins 28 and 29, respectively, in a freely rotatable manner.
When a workpiece is to be conveyed to a downstream pressing process, the feed and transfer device 25 is stopped from moving in the direction of the transfer line L, and first the workpiece, not illustrated, that is on the lower die 10 is engaged by the workpiece holder 19 attached to the cross bar 18 mounted on the feed beams. Next, the feed beams 14 which are suspended so that they are free to move in the horizontal direction along the press line L, the lift beams 13 that are free to be raised and lowered by the servo motor 11, and the rods 12 are raised, and the workpiece is removed from the lower die 10. The workpiece, that has been raised, is next transferred along the feed beam 14 by the feed and transfer device 25 until it is over the next lower die 10 on the downstream side of the press line L. Next, the lift beam 13 is lowered, the workpiece holder 19 is disengaged from the workpiece, and the workpiece is placed on the lower die 10.
However, the feed beam 14, suspended from the lift beam 13 moves in an arc with the radius R of the connecting rod 27 about the point O of the connecting pin 28 in the bracket 26 of the rack beam 24, when the lift beam 13 is raised and lowered (ascending in FIG. 1), that is, when the beam is raised from the position M to the position N, over a vertical distance H. This movement in an arc causes a displacement X of the feed beam 14, when it is lifted, because of the differential movement in the direction of the press line L due to the curved path of the press transfer motion. Likewise, the curved path of the press transfer motion also causes a differential movement when the feed beam is lowered. Normally, the workpiece must be raised and lowered perpendicularly with respect to the lower die 10. Otherwise, the workpiece may be deflected vertically, tilted or be displaced, so the workpiece will not be pressed and processed in the preferred manner. Consequently, the position of the rack has to be adjusted during the lifting operation, through a complicated correcting operation, which has been a difficult problem in practice.
FIG. 2 is a schematic view showing another conventional example known in the prior art. Unlike FIG. 1 in which the rack beam and the feed beam are connected by the connecting rod that moves up and down in a freely rotatable manner, in FIG. 2, the feed beam is connected to a vertical rod mounted on the rack beam, through a connecting rod that can be freely raised and lowered. More explicitly, the feed and transfer device 38 is composed of a servo motor 21 that moves the feed beam 35 which is free to move horizontally in the direction of the press line L, a pinion 22 rotated and driven by the servo motor 21, and a rack beam 37 provided with a rack 36 that engages with the pinion 22, on the upper surface thereof. The vertical rod 39 is installed on the lower surface of the rack beam 37 close to the end of the rack beam on the side facing the feed beam 35. The connecting rod 41 is provided with a slide bearing 40 that allows the vertical rod 39 of the rack beam 37 to slide through the connecting rod 41 so that it is free to move up and down. In this system, there is no movement in the direction of transfer of the workpiece, when the feed beam moves up and down. However, when the connecting rod is long, a deflection Y is produced due to the effect of gravity on the rod which is supported as a cantilever. Therefore, the vertical rod 39 cannot slide smoothly through the slide bearing 40, so that a runout or tilt occurs during raising and lowering in the same manner as described above, and the workpiece cannot be transferred easily, and in practice, this is experienced as a difficult problem.